<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        * {
            margin: 0;
            padding: 0;
        }

        ul,
        li {
            list-style: none;
        }

        .drop-down-box {
            width: 200px;
            height: 40px;
            line-height: 40px;
            color: #666;
            font-size: 14px;
            /* 子绝父相 */
            position: relative;
        }

        .down-tit {
            border: 1px solid #ddd;
            border-radius: 2px;
        }

        .arrow-box {
            float: right;
            width: 40px;
            height: 40px;
            background-color: #666;
        }

        .arrow-box::before {
            content: '';
            display: inline-block;
            width: 0;
            height: 0;
            border: 10px solid transparent;
            border-top: 10px solid #ddd;
            margin: 16px 0 0 10px;
        }

        .down-cont {
            background-color: #fff;
            border: 1px solid #ddd;
            position: absolute;
            z-index: 2;
            left: 0;
            top: 40px;
            /* calc 使用计算值 */
            width: calc(100% - 3px);
            display: none;
        }

        .drop-down-box:hover .down-cont {
            display: block;
        }

        .drop-down-box:hover .arrow-box::before {
            border-top: 0;
            border-bottom-color: #ddd;
        }
    </style>
</head>

<body>
    <!-- 原生 -->
    <div>身高：
        <select name="" id="">
            <option value="">136</option>
            <option value="">137</option>
            <option value="">138</option>
        </select>
    </div>
    <!-- 模拟 -->
    <div class="drop-down-box">
        <div class="down-tit">
            其他简介
            <span class="arrow-box"></span>
        </div>
        <ul class="down-cont">
            <li>关于作者</li>
            <li>鸣谢</li>
            <li>捐赠</li>
        </ul>
    </div>
    <div>新内容</div>
</body>

</html>